Add vscode devcontainer / testing setup

.devcontainer/Dockerfile

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+# See here for image contents: https://github.com/microsoft/vscode-dev-containers/tree/v0.154.0/containers/ruby/.devcontainer/base.Dockerfile
+
+# [Choice] Ruby version: 2, 2.7, 2.6, 2.5
+ARG VARIANT="2"
+FROM mcr.microsoft.com/vscode/devcontainers/ruby:0-${VARIANT}
+
+ENV DEBIAN_FRONTEND=noninteractive
+
+RUN \
+  apt-get update \
+  && \
+  apt-get -y install --no-install-recommends \
+    jq \
+    libjq-dev \
+    gnupg2 \
+  && \
+  sh -c "$(curl --location https://taskfile.dev/install.sh)" -- -d -b /usr/local/bin \
+  && \
+  curl -fsSL https://raw.githubusercontent.com/helm/helm/master/scripts/get-helm-3 | /bin/bash -

.devcontainer/devcontainer.json

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+// For format details, see https://aka.ms/devcontainer.json. For config options, see the README at:
+// https://github.com/microsoft/vscode-dev-containers/tree/v0.154.0/containers/ruby
+{
+	"name": "Ruby",
+	"build": {
+		"dockerfile": "Dockerfile",
+		"args": { 
+			// Update 'VARIANT' to pick a Ruby version: 2, 2.7, 2.6, 2.5
+			"VARIANT": "2.7",
+		}
+	},
+
+	// Set *default* container specific settings.json values on container create.
+	"settings": { 
+		"terminal.integrated.shell.linux": "/bin/bash"
+	},
+
+	// Add the IDs of extensions you want installed when the container is created.
+	"extensions": [
+		"ms-kubernetes-tools.vscode-kubernetes-tools",
+		"rebornix.Ruby"
+	],
+	
+	// Use 'forwardPorts' to make a list of ports inside the container available locally.
+	// "forwardPorts": [],
+
+	// Use 'postCreateCommand' to run commands after the container is created.
+	"postCreateCommand": "export RUBYJQ_USE_SYSTEM_LIBRARIES=1 && bundle install",
+
+	// Comment out connect as root instead. More info: https://aka.ms/vscode-remote/containers/non-root.
+	"remoteUser": "vscode"
+}

.vscode/extensions.json

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+{
+	"recommendations": [
+		"ms-vscode-remote.remote-containers"
+	]
+}

.vscode/launch.json

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+{
+    // Use IntelliSense to learn about possible attributes.
+    // Hover to view descriptions of existing attributes.
+    // For more information, visit: https://go.microsoft.com/fwlink/?linkid=830387
+    "version": "0.2.0",
+    "configurations": [
+        {
+            "name": "UnitTest - active spec file only",
+            "type": "Ruby",
+            "request": "launch",
+            "cwd": "${workspaceRoot}",
+            "program": "/usr/local/bin/bundle",
+            "args": [
+                "exec",
+                "m",
+                "-r",
+                "${relativeFile}"
+            ]
+        },
+        {
+            "name": "UnitTest - all spec files",
+            "type": "Ruby",
+            "request": "launch",
+            "cwd": "${workspaceRoot}",
+            "program": "/usr/local/bin/bundle",
+            "args": [
+                "exec",
+                "m",
+                "-r",
+                "${workspaceFolder}/test/charts"
+            ]
+        }
+    ]
+}